Shrink operations in progress can block other queries on the database, and can be blocked by queries already in progress.
Is this (blocking) applicable to both data and log files?
The question is so that the shrink activity can be planned during normal working hours or during maintenance window to prevent user/system issues caused due to the blocking.
For example - the following answer (https://social.msdn.microsoft.com/Forums/sqlserver/en-US/ed0db5ea-06a3-4a93-8ccc-362cfb94703d/would-manually-executing-dbcc-shrinkdatabase-block-the-database-?forum=sqltools) says the opposite of what is given in the above quote:
DBCC SHRINKFILE does not block operations in the database.