The 38B is needed as its the only service from Greenfield and Springboig to city centre. Its also the only service on Warriston Street.
The 46 provides a service from Castlemilk to Rutherglen and Parkhead, Bridgeton to Denistoun and Parkhead and Cranhill (its only bus service) and Greenfield/Springboig to Parkhead and The Fort.
These are important routes with very long established links but given the pressures on the bus industry these days you couldn't rule out some of these links being broken especially after whats happened to service 2. Hopefully it wont come to that.
I think the 38B and 46 are pretty solid services tbh. 38B is always been fairly busy and it's also the only link from Barlanark to Carntyne, bottom of Riddrie etc. The 46 has always been really busy too when I've been on it. Bit slow from Rutherglen to Parkhead but as it's the south part of Abercromby Streets only bus I highly doubt it'll go. Need to have at least 1 bus an area arguably and the 46 does a lot of areas with nothing much else outside of the middle of the route