There are very good reasons to separate data and log segments in all user databases, and especially tempdb. First being that ULC flushing to disk is done for every log record when you have mixed data and log segments, thereby bypassing the benefits of ULC. Additionaly, the separation of segments on to different devices allows you to tune for the different types of IO that occur for objects as different in that area as syslogs, and user tables. Also, isolating the capacity of the log segment from the capacity of tempdb tables can be very important. Managing those spaces separately is advantage, for example when establishing threshold procedures for space usage and monitoring.
Some would also go as far as separating the "default" segment from the "system" segment, as well as the "logsegment" all onto separate devices. Again, since "system" segments contain worktables, etc. those devices can be separate solid state or other faster service time devices apart from user tables on the "default" segment, or transaction log in tempdb.