O motivo pelo qual você está tendo um atraso ao usar less +F é este (tirado de esta resposta , o que é tão bom que vou citá-la textualmente):
less +Freads the whole file, whereas on many systemstail -fonly reads the end of the file, and even on the systems where it does read the whole file, at least it doesn't keep the whole file in memory. That makesless +Fimpractical for very large files. You can however runless -n +F, which causes less to read only the end of the file, at the cost of not displaying number.Under the hood, between
less -n +Fandtail -fdoes, the main difference is thattailuses a file change notification service on some platforms (e.g. inotify on Linux), which allows it to display new data instantly, whereaslessmight take up to 1 second to display the new data because it checks for new data in a loop and sleeps between checks.