Pros and cons of a single supermemo collection

There is no good and right about having one single collection or several for SuperMemo. You may decide when it is best to start a new collection, merge collections, or transfer branches between different collections according to many factors and current needs.

Interleaving

Video/audio repetitions break the flow

Stats

Averages may be not representative

Backup

Using the built-in backup solution is increasingly inefficient as collection count grows. You would need to backup each collection one by one. It makes close to no difference if you are using a git solution for backup, as I do strongly recommend to do.

Searches

Searches are done in assembly language for maximum speed. Even tough, when you reach large volumes you can appreciate the delay. Therefore, having a single collection will foment larger volumes of text and other registries making searches slower. It will make a difference if you are strarting a new collection for learning a language and perform searches very often. One exception would be English language, as it is the vehicular language for Incremental Reading. The same would apply if you are using another language instead of English.

Collection parameters

Same collection parameters for different difficulties

Final Drill

Having multiple collections make the selective final drill very accesible, as you can turn on/off the finall drill for each collection. For instance I could turn it on for language learning collections. Having a single collection makes the finall drill a everything or nothing choice. There is a word-around by creating subset reviews from the drill queue (video).

Priorities

Requires more precision for prioritization