Steven P. McNicoll writes:

Required to accommodate IFR? If traffic or SUA does not allow the
issuance of that IFR clearance to climb through the clouds it's not
going to be issued.

ATC cannot deny service to IFR flights once a clearance has been issued, so
once you've started your IFR flight they cannot cut you off. Flight following,
on the other hand, is at the discretion of ATC, based on the controllers'
workload and other considerations. So, while you're guaranteed to continue
getting IFR services once you've got them, if you cancel IFR and then request
flight following, there's no guarantee that you'll get it.