It depends on what internal resources the technicians use when they're in the field. For our remote staff, we've found that the advantages of having them as part of the domain out-weigh the occasional hassles of dealing with domain access over slow connections.
We have a bunch of small remote offices (some are just home offices) with staff who come in only a few times a year. About 20 staff in total. But they use email (Exchange), access internal web sites, and use files on network shares, so they're set up as part of the domain and access everything over a VPN connection.
One big advantage of having them as part of the domain is that when they do come into a main office, they usually need to access a lot of stuff in a hurry - print stuff on the bigger, better printers in the main offices, copy a bunch of files back and forth, try out new applications, get a tune-up on their laptop. All of this is much much easier when they're a member of the domain.