I have several beds of azaleas and rhododendrons with grass running up to and into the beds. Every year or two, I have to edge the grass back six inches or more as the shrubs grow. If perennials are planted in the same beds as shrubs, you may have to dig up, divide and replant the perennials, giving the shrubs more room. The cottage garden look may suggest that plants should intermingle, but not so dramatically that you cannot identify the individual specimens. This doesn't mean separating them completely.
Separate plants look like unnatural afterthoughts.
A neighbor lined the front of his yard with a mound of topsoil and bark, and planted a heather every six feet. It looks just like the Civil War battlements I saw in Tennessee. Every time I look at his yard, I expect to see a sprawled trooper and a muzzle peeking over the mound or around one of the bushes. Crowded shrubs look like a single mass. Appropriately spaced shrubs will still merge but continue to display their individual shapes.