Someone in this topic mentioned that a musician would be offended if someone referred to what he does as making beats. The thing is, some music producers refer to what they do in a likely manner – especially, those beatmakers who are making a living this way (I didn't investigate much, but you can earn some quite substantial income if you're good at it) and those a part of hip-hop subculture. Talking specifically, in the most genres beat doesn't make a whole arrangement, but in hip-hop it does and so the higher the requirements are.
Well, to dot the i's and cross the t's, here what Wikipedia says:
A hip hop instrumental is casually referred to as a beat, and a hip hop producer is casually referred to as a beatmaker.
And, again, there is a genre of instrumental hip-hop (quite interesting one, should I say), in case of which a beat makes 100% of arrangement, for reasons quite obvious.
To answer the initial question, a musician does need how to make beats if he composes music on his own, which is a common situation for anyone involved in electronica, especially inspired by jazz, funk, or hip-hop – i.e. genres which necessitate a good groove.
And the last thing... From my experience, a beat is something you rather not pay no regard to while composing. I mean, the more complex and detailed it is, the more interesting harmony you can build upon it. A beat serves a basal complex of a track in a way. With no regard to whether a musician is good at jamming or punctilious composing, a daedal beat (or rhythm section) will force him to play more inventively, thus routing a mechanical activity into a more intelligent raceway. I think this has to be considered important, as expanding the boundaries of own playing patterns is vital. Otherwise once enthralling pursuit can become a purely motoric exercise and showing off of fingers' dexterity.
