If you are not regularly backing up the transaction logs, the log won't free up any space. It will hold onto all the space it has (and can get) and keep the transactions in there. Therefore, a shrinkfile operation will look just look at the log and say "no free space to shrink" and finish without actually doing anything.

That depends on your system setup. Is it an OLTP or a data warehouse? How often are transactions getting pushed into the database? How much data can be lost if the system goes down?

Depending on those factors, a "regular" transaction log backup can be anything between once a day to once an hour to once every 15 minutes. At my workplace, we have some DBs that have a once an hour log backup during business hours only, some DBs (Simple mode) that have no log backups at all, and some DBs that have a log backup once every 4 hours during the 24 hour day. It just depends on what the databases are doing, how often updates happen, their recovery mode, etc.