In a video interview in 2014, West Ham chairman David Gold said:
I am a great supporter of safe standing, it is interesting that for many years we have had unsafe standing, we do have that, I don’t think there is a ground in the country that are all seater stadium that don’t have their fans in some area of the ground standing.
Right now in most football grounds, many of the most enthusiastic fans will stand throughout the match, notwithstanding the all-seater nature of Premier League and Championship stadia. There are regular squabbles with security stewards but staff mostly turn a blind eye. As Gold points out, this is dangerous, as supporters will regularly fall over the seats in front of them into the next row.
It also causes steady, attritional damage, especially when particularly exuberant away supporters visit—as with a recent cup tie that brought Manchester United to Derby:
United will be asked to compensate Derby County after a significant number of seats were damaged in the away end when the teams met in the FA Cup fourth-round at the end of last month, resulting in a 3-1 win for Louis van Gaal’s team.
Derby have already informed United about what their groundstaff found on the morning after the match and intend to charge them for the relevant repairs, claiming that more than 300 seats were broken or pulled off whole.
Each match can cost thousands—peanuts in Premier League money but still a cost worth considering, especially when there's an alternative. Safe standing alternatives such as rail seats do not have breakages that require replacements every week; the seat is tucked away, clipped off or much harder to break.
Of course this isn't the main reason to favour a relaxation of the rules, allowing clubs in the top two tiers to emulate Germany, Sweden, Austria and the lower tiers, where standing has been safely allowed. Fans cite the more intense atmosphere that standing allows for (just look at the Yellow Wall above).
But perhaps more important is simply allowing for higher attendances. The recent Kop walkout over ticket prices was just the latest example of the rising fervour against the ticket prices Premier League clubs charge. Terraces can fit in as many as 1.8x times as many spectators—safely. Not only could greater total supply bring down ticket prices overall, but more variation in the 'products' that clubs can offer fans means they can price discriminate. Well-heeled neutrals and tourists can pay hundreds to sit; core fans can be offered cheaper season tickets.
But either way, after a long hiatus, it may be that safe standing in stadia is an idea whose time has come again.