Does it matter who issues the petition for the divorce?
The outcome (the dissolving of a marriage/civil partnership) will be the same no matter who the petitioner or respondent is.
The main advantage in being the petitioning party is that you have an opportunity to take the initiative; control the timetable (the speed of proceedings); choose which ground applies to your divorce/civil partnership dissolution; when to apply for a decree nisi/absolute or conditional order/final order and so on. The petitioner is also able to seek a court order demanding that their spouse/civil partner (the ‘respondent’) pay their legal costs.
The main disadvantage in being the petitioning party is that you will have to conduct the proceedings in respect of paperwork and you will initially be responsible for any court fees.
It is usually prudent to establish a sensible dialogue with your spouse/civil partner so that all matters are agreed before you send your petition to the court. This will minimise any unnecessary unpleasantness between parties and limit costs and delays.