The only reasons I can think of to use ALT HOLD is if for some reason you suddenly have a requirement to hold a passing altitiude in the climb/descent, and on some aircraft it may be a recommended pitch mode in severe turbulence.
Depending on your aircraft type the mode can have several traps - As others have said if you do insist on using the mode you've lost the FMC speed scheduling and you are not latched to the altitude/FL in the MCP window, you are holding the altitude at which you pressed the button.....
This of course is all subject to the advice your own Company's FCOM - what does that say?