insgesamt
overall
Expresses a summary or the overall result; all things taken together, considered as a whole.
Wir haben insgesamt 250 Euro für die Geschenke ausgegeben.
We spent a total of 250 euros on the gifts.

overall
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overall
Expresses a summary or the overall result; all things taken together, considered as a whole.
Wir haben insgesamt 250 Euro für die Geschenke ausgegeben.
We spent a total of 250 euros on the gifts.

The word is made up of 'in' (in) and 'gesamt' (whole/total). 'Gesamt' means 'ganz' (whole) or 'total' (total). The meaning 'alles zusammengenommen' (all things taken together) can therefore be derived directly from its components.
Die Renovierung hat insgesamt drei Monate gedauert.
The renovation took three months in total.
As an adverb, 'insgesamt' (overall/in total) is flexible. It can stand at the beginning of the sentence in position 1, which triggers inversion (verb in position 2). But it can also stand after the verb in the middle of the sentence.
Insgesamt war der Urlaub sehr schön.
Overall, the vacation was very nice.
'Insgesamt' (overall/in total) is typically used to take stock or give a summary. It often introduces a sentence that contains a final result, a total sum, or a concluding evaluation.
Wir haben drei Pizzen bestellt, das macht insgesamt 35 Euro.
We ordered three pizzas; that makes 35 euros in total.
big / great
'im Großen und Ganzen' and 'insgesamt' have a similar function: both summarize something and do not look at every detail individually. 'insgesamt' is a normal adverb and works well when you are giving a result or a total number. 'im Großen und Ganzen' is a fixed expression and often sounds like a general assessment: there may have been small problems, but the overall picture is what matters. 'insgesamt' is shorter and more neutral, while 'im Großen und Ganzen' sounds a bit more explanatory.

Insgesamt haben heute zwölf Personen an der Besprechung teilgenommen.
In total, twelve people took part in the meeting today.
Im Großen und Ganzen war der Kurs gut organisiert.
By and large, the course was well organized.