I have been wearing a sleeve while I sleep for roughly 6 months with no negatives. Its not a tight sleeve, very comfortable and easy to sleep in. No negatives when I get erect during the night or in the morning. Since I am a side sleeper the sleeve alone has enough weight to where I feel longer in the morning. I also wear the sleeve all through the day as well except when doing actual PE.
My flaccid length has dramatically changed and my erect length is progressing also. Highly recommend adding it in. The sleeves are inexpensive, easy to use and they dont cut off circulation.