We have had mixed luck with loan. Going back people like Pique and Richardson had good moves but Rossi didn't get a game at Newcastle. This season CBJ can't get a game at Wolves. http://football-wonderkids.co.uk/2017/03/football-loan-market-sweet-science-clubs/ I think B teams would be better or sending a maximum of 5 players to a feeder club.
Overall I think it helps to the young players. They get a chance to actually play and gain experience instead of just sitting on the bench of the bigger club.
Yes, I believe for young players it's a great opportunity to get first team experience. Especially for talents signed in top clubs. For example Andreas Christensen (CB) from Chelsea who joined Mönchengladbach on a 2-year loan. Have played regular on their first team squad for almost 2 years in the Bundesliga in the aged of 21.
Loaning players out is a great opportunity for both the clubs involved and player himself. The player can progress playing week in and week out, prove himself and impress the manager at the parent club to recall him. The loanee club most of the times get a half decent player with bags of potential that helps them to survive in the league or qualify to the premiership. However sometimes players rest on their laurels and don't do enough to be in the starting XI of their new club. They don't get enough game time as a consequence and so it is termed as a failed loaned spell.