First: you will not be knocked out!
Weekend congresses are run on Swiss lines in which players play every round, in each of which they play someone on a similar running score. Further, in most congresses it is possible to claim a ½ point bye at the time of entry in any round other than the last. Very useful if you cannot make a Friday evening start, have a prior commitment for part of the weekend or simply don't fancy playing every round.

Second: you will not be duffed up by the big boys, unless you want to be.
Congresses are divided into sections.
Usually this entails an open section which anyone may enter, plus a number of other sections each with an upper grading limit for entry. Consequently you can arrange to play people your own size if you wish. These sections are typically given names such as major, intermediate, minor, novices. However there is no standard grading limit associated with each name. For example the major at Frodsham is for players graded under 170, at Blackpool the major is for players graded below 140.
However there are a few congresses at which the players are divided into sections by the organisers once all entries are in. This is usually done to enable them to guarantee small sections. Leek employs this system to create sections of about two dozen outside of its open; Blackpool, which doesn't use this system, can have sections in excess of 60 players. As entrants under this system do not know at entry whether they will be one of the top, middle or lowest graded players in their section, it discourages "pot hunters". This, together with the small section size tends to encourage a friendly atmosphere.

Third: you need not get bored between rounds.
Congresses provide an analysis room in which you can go over your game with opponent or friends, refreshment facilities and usually a bookstall. The published timetable of sessions means that you do not need to hang around the venue between games - you may well find time for a spot of sight-seeing or shopping or for a leisurely meal in a local restaurant or hostelry. Indeed rates of play are slower than in most leagues, typically allowing an average of 2½ minutes per move to the first time control, so an early finish can give you ample time to get out and explore.

Fourth: an incentive - do well and you can win a prize.
Organizers try to return as much money in the form of prizes, usually cash ones, as possible. Apart from prizes for those filling the leading places in each section there are often grading prizes for the best performance in a section by someone whose grade is below a declared value. Also you may come across fast-riser prizes for people who do best after a poor start, or for juniors, veterans or ladies.

There are a large number of weekend congresses in existence, most of which are listed alongside one day quickplay events and a few longer congresses in one of the calendars referred to on the links page.