really, unless you record with a click or metronome, it is just too much hassle to mark out points and stretch or warp, or so on.
such painstaking work.
if you use digital/electronic gear, this will not be an issue. just type in the beats per minute and the grid will be pretty much pefect.
if you have to adjust it, you need only do it once for the whole recorded track.
on the other hand, if you are not using digital/electronic gear, but for example an electric or acoustic guitar you really need to have a click (this is really what is called a metronome) to keep you in time as you will save so much time by dong so for yourself, and everyone else involved.
a free piece of software which will count bpm for you very accurately if needed is called Mixmeister, and the free version allows highly acurate bpm count.
though, again, unless you have a perfect ear for time and can play like an electronic device you will still need to mark out and warp each section of the piece. (HASSLE)
likewise traktor 2 and other pro dj gear will count the bpm accurately for you. but you'll still have the same issue unless you use a form of metronome to keep you in perfect clock ticking beat.
i know many musicians slag this "mechanical" timing off, but really, it makes a hell of a difference to your work and work time, makes life easier for you and workmates.