Formula activate only when data is there

I am having data in only column A. But numbers of data are not fixed. They are as large as 50000 and as small as 50.

On these data I use formula to extract data. But If I assume that i will have 50000 entry and If i use formula for all these entry workbook take much time to open and save.

I want to know is there any trick that formula will activate in adjust-en column only when there is data in coumn A.

I have data in A column.
I am using formula in B,C,D,E and so on column.
Now suppose I have only 50 data. I want, formula entered in column b,c,d,e activate for only up to row no 50 only.

Kindly help.
Regards,
PN

Please find attached file herewith. In the file record is upto A17202 cell. I have formula in B column. I want formula will activate only when there is data beside cell in B column. I required this as file take long time to open and save.
Regards,
PN