When is GRBLHAL not the right choice?

[HubertBloom]

What types of projects is GRBLHAL not suited to??

Is it limited to steppers and not servos?
Is it limited to open loop steppers and not closed loop?
Are there other considerations that make it unsuited to certain types of CNC machines?

[phil-barrett]

Works with anything that supports step/direction input. A number of boards support servo alarm/error output. A lot of users have servos and CL steppers.

What are you looking for? grblHAL has support for a pretty broad range of applications.

[terjeio]

Are there other considerations that make it unsuited to certain types of CNC machines?

A few gcodes are not supported, notably G41 and G42 (cutter compensation) and G61, 664 (path modes). These do not pertain to certain machines though, rather than to their use. Not suitable could be machines with tool heads (spindles) that can be rotated?