There once was an item

Question

...It was pretty darn flat

Some people may even call it a mat

Supporting an integral tool to some, yet a dying tool to many

At least compatibly, it supports any!

Making it easier to move, even to be precise

To its beneficiary's homograph, you probably won't be nice

It's used at home, in the office, but rarely on the road

Some even aren't flat at front, to support the user's load

But the largest portion is, or else there'd be no point

One last clue might be pain, in a specific joint

Side note: This is my first post here, so any feedback is welcome/appreciated

Answer 1

There once was an item

A mousepad

...It was pretty darn flat

Usually!

Some people may even call it a mat

aka mouse mat

Supporting an integral tool to some, yet a dying tool to many

I use one every day, but touch screens are getting more popular

At least compatibly, it supports any!

A mouse pad isn't picky

Making it easier to move, even to be precise

It helps with mouse movement + precision

To its beneficiary's homograph, you probably won't be nice

The beneficiary is the mouse, i guess, and most people don't like (living) mice.

It's used at home, in the office, but rarely on the road

True enough

Some even aren't flat at front, to support the user's load

Many modern mouse pads have a raised section to support the wrist

But the largest portion is, or else there'd be no point

Yeah

One last clue might be pain, in a specific joint

Prolonged use of a mouse can cause RSI in the wrist.

Answer 2

Is it:

A table/desk

1. It was pretty darn flat

   A table is pretty darn flat.

2. Supporting an integral tool to some, yet a dying tool to many

   This is why I included desk. A desk supports tools. Dying tools could be paper/pen as they are being replaced by computers.

3. At least compatibly, it supports any!

   You can stick whatever tools you want on a table or desk.

4. Making it easier to move, even to be precise

   Desks allow precision when working, not too sure about moving easier.

5. To its beneficiary's homograph, you probably won't be nice

   No idea.

6. It's used at home, in the office, but rarely on the road

   Desk at home, desk in the office, no desk in car.

7. Some even aren't flat at front, to support the user's load

   Shaped desk to prevent pens etc rolling off, or maybe shelves attached? Not too sure on this one either.

8. But the largest portion is, or else there'd be no point

   Desks would be useless if they weren't flat

9. One last clue might be pain, in a specific joint

   People kick their desks and tables all the time, the joint could be your toe.

Not too sure on this one, cool riddle!

Answer 3

I don't really feel like this is better than Zen Monkey's answer, but worth a shot. Is it

a bed?

...It was pretty darn flat

Beds are pretty flat

Some people may even call it a mat

Some people sleep on bamboo or foam mats, that's pretty much what college dorm mattresses are

Supporting an integral tool to some, yet a dying tool to many

Not really sure about the "tool" part, but many people die in bed.

At least compatibly, it supports any!

Anyone can lie on a bed

Making it easier to move, even to be precise

Perhaps a hospital gurney? Makes it easier to move someone who is incapacitated

To its beneficiary's homograph, you probably won't be nice

No idea about this one either

It's used at home, in the office, but rarely on the road

People generally sleep at home. Office is a bit of a stretch, but maybe a doctor's office? In vehicles there are not usually beds, unless you're in an RV

Some even aren't flat at front, to support the user's load

Some beds like Sleep Number beds can be tilted at the upper body for greater comfort. Also hospital beds can usually be raised.

But the largest portion is, or else there'd be no point

The majority of the bed is still flat and horizontal

One last clue might be pain, in a specific joint

Not sure about "specific", but joint pain often makes people stay in bed longer