This varies on what look you want and the different installation, so you must consider the reasons for sealing. Sealing pavers is similar to varnishing timber. The benefits are, it will hold the depth of colour, especially for darker coloured pavers, it will help protect the pavers from staining, make them easier to clean and reduces the amount of fungal and mould growth. Alternatively, by not sealing, the pavers will age and weather naturally. There is also some ongoing maintenance.theywill need to be resealed every 2 – 10 years (depends on type of sealant, usage and environment). There is no right or wrong between sealing or not, - you need to consider what you are trying to achieve by sealing the pavers.